Re: aq260a timing
this is a copy from another volvo penta thread. hope it helps you.
Many will set BASE advance and not check any further.
We start and idle on BASE advance only... that's about it.
The progressive ignition advance is much more important for a good running SBC Marine Engine.
It can also be very destructive if not correct!
(too much advance and/or too early, and we risk detonation damage)
To check this, the engine rpm must be taken up to the limit rpm, as the timing marks are strobed.
This spec must be known for the engine that is being ignition timed.
Volvo Penta workshop manual that includes the 260A engine.
T?NDSYSTEM
T?ndstift ........................................................................................ Bosch HR 8A
T?ndstiftsgap ................................................................................ 0,7 mm (0.028")
T?ndf?ljd ....................................................................................... 1-8-4-3-6-5-7-2
Grundinst?llning ............................................................................ 8? f.?.d. (B.T.D.C.)
Stroboskopinst?llning 4200 r/m .................................................... 30? f.?.d. (B.T.D.C.)
Kontaktgap, mm (in) AQ200D, 225D, 260A .................................. 0,36?0,48 (0,014?0,019)
AQ290A ........................................................ 0,25?0,36 (0,01?0,014)
Slutningsvinkel AQ200D, 225D, 260A .......................................... 28??34?
AQ290A ............................................................... 29??32?
(the last numbers I believe are dwell angle)
The Volvo Penta AQ 260A specs on page 30 (above) are rather vague in one area.
They show a total advance of 30* @ 4,200 rpm.... but do not show us what the advance is at 3,200 rpm where many specs will.
If the 30* was held back, and would not be "full In" until 4,200 rpm, performance may suffer, IMO.
Ideally you'll want to find the correct 260A curve (similar to the one below), or at least some clear specs for this engine showing what occurs at/near 3,200 rpm.
28* @ no earlier than 3,200 rpm is going to be very close.
26* @ no earlier than 3,200 rpm is going to be more conservative!
This advance curve graph is an example only.
BASE is not shown in the vertical scale, and will not be accounted for in the linear curve graph.
It must be added in order to know what the TA number will be.
However, when checking dynamically, BASE can't help but be included, as it will be part of what the strobe light sees.
